DOE EYED: "John Doe Duffel Bag" was apparently filmed near the 99-cent store where Isaac Kadare was killed and near the shop where Rahmatollah Vahidipour was slain. Photo:

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A mysterious man toting a duffel bag has been identified as a key “person of interest” in the Brooklyn serial-killer case — after surveillance video showed him at one and possibly two of the three slay scenes, law-enforcement sources told The Post yesterday.

Cops said they are eager to talk to the mustached man — whom they dubbed “John Doe Duffel Bag” — about the killings of three Middle Eastern shop owners, each shot with the same .22-caliber gun over the last four months.

The unidentified man, who is middle-aged, white and balding, was most recently caught on surveillance video, duffel bag in hand, at around 6 p.m. Friday near the Flatbush store where owner Rahmatollah Vahidipour, 78, was found dead at 7:11 p.m., cops said.

Another video appears to show the same man near a Bensonhurst shop on Aug. 2 around the time its owner, Isaac Kadare, 59, was killed there, several sources said.

The duffel man has no known connection to the first murder — of shopkeeper Mohammed Gebeli, 65, in his Bay Ridge clothing store on July 6.

“We want to identify the man known as John Doe Duffel Bag,” said NYPD spokesman Paul Browne.

A law-enforcement source said, “The duffel-bag guy could be a perp, or he could be a witness.”

“Duffel Bag” was one of four people caught by surveillance cameras near Vahidipour’s murder. Cops released their images Sunday.

Browne said cops have learned two of them — a running man and woman — were a vendor and a woman who had allegedly stolen perfume from him.

The fourth, an older woman, has nothing to do with the case, Browne said.

The FBI’s famed serial-killer profilers have joined the hunt for the psycho.

“We’re talking to the FBI and going all out to stop these murders,” Police Commissioner Ray Kelly said as the combined reward for information about the killer hit $84,000.

Kelly said “it’s reasonable to assume” the killer conducted “reconnaissance” on the victims, all of whom were alone in stores that didn’t have cameras inside.

Money was stolen in the first two killings, but nothing was taken in the third. Vahidipour had $171 in his pocket, a source said.